1. Field of the Invention
The present invention relates to a wet section of a machine for producing a fibrous material web, specifically a paper or a cardboard web, which includes at least one press unit that includes a nip through which the fibrous material web, which has been preformed in a web forming section, is guided.
The present invention also relates to a method for treating a fibrous material web in an elongated nip of a press section of a machine for producing a fibrous material web. The method includes preforming the fibrous material web in a forming section of the machine, guiding the fibrous material web, which has a dry matter content of approximately 15%, to at least one elongated nip and pressing the fibrous material web in at least one elongated nip.
2. Discussion of Background Information
The wet section of machines for producing a fibrous material web, particularly for producing either a paper or a cardboard web, occur after the web forming region and after the fibers have achieved a certain immobility gradient. Further drainage of the wet fibrous material web has, in the past, primarily been achieved by elements that essentially operate through the use of suction, such as, for example, particular foils, register rolls, suction boxes, suction rolls, or the like. Connecting this type of drainage to the machine incurs considerable expense, especially where, for example, the element requires a large amount of space or, for example, where generating the vacuum consumes an excessively large amount of costly energy. In addition, depending on the type of material, the drainage screen, which rubs over the mostly stationary drainage elements, may result in a relatively short screen service life.
In a wet section of the type discussed in EP-A-0 359 696, a press function is integrated into the screen region to eliminate a web pick-up point. The press point provided in the screen region includes a suction roll and an open roll. Either the relevant nip is not very hard, i.e. having a high linear force, or the nip is very short and soft, which can be attributed to a low linear force. Neither of these operations is suitable for removing the required quantity of water from the fibrous material web with the lowest possible pressure gradients when there are low dry matter contents, i.e. when the fibrous material web is still wet.